Embedded element sole plate



Oct. 31, 1950 H. F. STORM EMBEDDED ELEMENT SOLE PLATE 5 Sheets-Sheet 1Filed July 20, 1944 biy f nmi Oct. 31, 1950 H. F. STORM 2,528,019

EMBEDDED ELEMENT SOLE PLATE 3 Sheets-Sheet 2 Filed July 20, 1944 Oct.31, 1950 STORM 2,528,019

EMBEDDED ELEMENT SOLE PLATE Filed July 20, 1944 3 Sheets-Sheet 3Patented Oct. 31, 1950 2,528,019 EMBEDDED ELEMENT SOLE PLATE Herbert F.Storm, West Allis, Wis., assignor to Sunbeam Corporation, a corporationof Illinois Application July 20, 1944, Serial No. 545,789

This invention relates to electric sadironsyand the sole plate in thecasting thereof. The. construction is such as to possess relativelylight weight with strength and durability for the purposes intended. Thesole plate structure also provides for uniformity of temperaturedistribution due in part to the characteristics'of the materials usedand to the form of the embedded. element and its heat transfer relationto the surrounding metal body in which it is cast.

Another object of the invention is to provide a new and improvedembedded heating element especially adapted to be, cast in a metal soleplate and havingnovel form and construction I characteristics which make,it a goo'd heatfconductor and a poor electrical conductor at elevatedtemperatures, andwhich will maintain its shape.

and form without cracking while being subjected '2 Claims. (o1. 2195-25tothe drying and vitrifying processes in' the course of its manufacture,and which has sufii cient mechanical strength. to permit of its being,handled in production and being subjected to' the casting process.

Another object r my invention is to provide a new and improved method ofmaking a ceramic heating element having an embedded electric resistor. 1h Another object of my invention is to provide a new and improved methodof making a sole plate for an electric iron.

Another object of my invention is to provide a new and improved soleplate of the character described with the view to moreeconomicalmanufacture.

Other objects and attendant advantages will be appreciated by thoseskilled in this art as the drawings, in,

Fig. 3 is alongitudinal section taken substantially on the section line3-3 of Figure 1;

Fig. 4 is an end elevation, looking at the heel end of the sole plate;

Figs. 5 and 6 are sections taken on the section line 55 and 66,respectively, of Figure 1;

Fig. 7 is a top view of a ceramic heating element embodying myinvention;

Fig. 8 is a side elevation of the heating element, partly in section onthe section line 88 of Fig. 7;

Fig. 9 is a fragmentary section showing a modified form;

Figs. 10, 11, 12, 13, and 14 are fragmentary views showing steps in themanufacture of the ceramic heating element, the sections being takensubstantially on the section line I0I0 of Fig. 15

L1 coaction of other die parts with the bottom die;

Fig. 15 is a top view of the bottom die;

Fig. 16 is a bottom view of the top die;

Figs. 17, 18,19, 20, and 21 are cross sections through certain of thedie members used in forming the ceramic heating element; and

Fig. 22 is a top view of an insert die member, which die members will bepresently described.

An illustrative embodiment of the ceramic heating element is shown inFigures 7 and 8. This is a preferredembodiment intended forincorporation in a sole plate substantially of the design shown. inFigure 1. 'It should be understood, however, that inthe practice of myinvention the ceramic heating element will be of such size andproportion as to conform with the sole plate into which it is to becast, bearing in mind the novel characteristics and functions of theceramic heating element'which will now be described. erally by 25 iscomposed of a ceramic refractory material which is formed to askeleton-like shape constituting a self-supporting body having por tionsof relatively small cross section within which an electrical resistordesignated generally by 26, preferably helical, is embedded. Accordingto my invention the ceramic element is formed to provide a continuousouter body portion made up of what may be termed longitudinal outerbody, portions 21 and 28 joined by toe and heelfl portions 29 and 3i,respectively, longitudinal in- The heating element designated gene norbody portions 32 and 33 spaced laterally from each other and from thelongitudinal outer body portions, a portion 34 connectin the portions 32and 33 with the toe portion, and a plurality of narrow portions 35, 36,31, and 38 connecting the inner and outer longitudinal body portions.The helical resistor element 26 is arranged to extend continuouslythrough the longitudinal body portions from the input to the outputterminals 39 4|. Assuming the resistor input terminal is at 39, theresistor extends continuously through the body portions 21, 29, 28, 3|,32, 34, and 33, to the output terminal 4|. In order to firmly andpositively locate the terminals 394| against displacement and toposition them in definite relationship to the thermostatic switchmechanism (not shown) which controls the flow of electric current to theresistor, I have provided ceramic inserts in the form of cylindricalposts 42 each preferably formed to provide an enlarged base end 43 and atapered or chamfered top end 44. Similar ceramic posts 45 are insertedin the connecting body portions 35 and 36. These posts 4 245 serve aslocating and supporting elements when casting the ceramic heatingelement in the aluminum or other metal body which constitutes the soleplate proper, as will be presently described. The body portions of theceramic heating element are arranged to give good heat distribution whenthe element as a whole is cast in the metal sole plate, and as aconsequence of this construction the sole plate proper will assumeuniform temperature substantially throughout its ironing surface and theheat transfer will be direct and efiicient. The cross sectional shape ofthe body portions may be prismatic such as square as shown generallythroughout the drawings, or round as shown in the modified form Figure9. In the functioning of the completed sole plate the cylindrical formof the element 25 would require a slightly lower temperature for thehelix than with the square cross section but the die and mold cost arelower with the latter form. Also, the square cross section hasadvantages in its mechanical strength and in connection with itsmanufacture, as will be presently apparent.

The ceramic heating element in addition to its self-supporting shape andpermanency of its structure, is composed of a material which will serveas a bond between the electrical resistor (such as a nichrome wire) anda cast metal shell or body which constitutes the sole plate proper.According to my invention the material composing the body 25 should havehigh thermal conductivity so as to be a good heat conductor between theelectrical heatingv element and the metallic sole plate. It should alsohave high electrical resistivity so as to be a poor electrical conductorat the elevated temperatures such as are encountered in high wattageautomatic sadirons under thermostatic switch control. The materialshould have sufiicient mechanical strength to permit handling inproduction and so that it will not be destroyed or impaired mechanicallywhen subjected to the metal casting process. It should have no tendencyfor developing cracks while being subjected to the drying process andlater to the vitrifying process in the course of making the ceramicelement. A material which I have found suitable for this purpose is arefractory high temperature cement kown as Alfrax 13. In practice I haveobtained good results by mixing this material with 4.7% of water byweight, making a plastic cement. I have found the water percentagerather critical in obtaining the resultant char acteristics abovedescribed. If less water is used the cement crumbles; and if more wateris used the material is too soft when taking it out of the mold and issticky and difficult to handle.

The manufacture of the ceramic element will now be described, referringmore particularly to Figures 10 to 22 inclusive. The mold or die partscomprise, generally stated, a bottom mold 46, an insert die member 41, atop mold 48, a pressure die member 49, and an ejector member 5|. Thebottom mold has a cavity 52 of a shape identical with the describedprofile shape of the ceramic heating element 25, so that the profile oroutline shape of this cavity determines the corresponding shape of thebody to be molded therein. The cavity 52 is of substantial depth asshown in Figure 10 and the side walls are vertical, with slight draft.The die member 41 also conforms with the shape of the ceramic member 25and is adapted to be inserted in the cavity 52 so as to rest at thebottom thereof and constitute the bottom proper of the cavity. After theplastic mold is completed this bottom member 41 will be raised to ejector discharge the plastic molded member by means of the ejector diemember 5| which is equipped with a plurality of pusher pins 53 which areadapted to be moved up through the bottom of the cavity for liftin theejector member 41 to the ejecting position shown in Figure 14. The firststep is to fill the cavity 52 with the described plastic material 54, asshown.

in Figure 11. The next step is to apply the top mold 48 in .a materialdisplacement operation shown in Figure 12. It will be apparent that the7 top mold is provided with projecting mold members 55 shaped todisplace the plastic material to provide a cavity 56 therein conformingin outline with the outline shape of this projecting mold body showninFigure 16. The cavity 56 formed in the plastic material is for receptionof the helical heating element 26 and also for the reception of therefractory holders 42 and 45,

it being observed that the top mold has portions 57 Which provideproperly located cavities for the reception of the wide lower ends ofthese refractory holders. In actual practice the face of the upper moldis covered with a thin film of machine oil or a similar oil tofacilitate parting from the plastic material when drawing the mold andalso a suitable vibrator (not shown) is applied to the mold when makingthe draw. The next step is to place the helical resistor wire inthecavity 56 and the refractory holders 42 and 45 in the correspondingcavities in the plastic material, the holders 42 being strung on theterminal ends 39 and 4| of the resistor wire which is bent to conform tothis location of the holders as will be obvious from the location shownin Figure '7. it will be filled with the same refractory cement as usedfor the body, except that I prefer to use a slightly greater moisturecontent. This makes the material more plastic to facilitate filling thehelix by rolling it through the cement. The next step is to apply thepressure die member 49 which has projecting mold members 58 shaped tofit into the main cavity 52 in a plunger action completely covering 'theplastic material but Without disturbing the'refractory holders. Thisoperation is performed in a press under sufficient pressure to displacethe plastic material from' the side walls and dispose it in a compactbody about the helical walls, filling all voids and inter- However,before inserting the helix stices and making intimate contact betweenthe plastic material and every point on the surface of the wire. Thiscompression gives the final cross sectional shape to the heatingelement, as shown in Figure 13. The pressure die is then withdrawn andthe ejector die operates to raise the heating element to an elevatedposition as shown in Figure 14, from which the heating element may beremoved for transfer to a drying station. Tofacilitate removal of theplastic heating: element from the bottom member 41v a layer 59 of paperor an equivalent is applied to the face of said member. This paperfacing remains on the bottom member and prevents sticking of the plasticmaterial. The plastic element at this stage is sufiicientlyform-sustaining as to permit of its being picked up by hand and placedin a position for drying. The drying may be accomplished by air or byapplying a reduced voltage to the heating element so that the moldedbody reaches a temperature of about 212 F. in about an hour.Acceleration of the drying process beyond this may result in cracking ofthe molded form. Following this the molded element is put in a furnaceand heated to about 22002300 F. for about an hour. This vitrifies theceramic heating element, and produces a hard form-sustaining body inwhich the resistor wire and the refractory bosses are permanentlyembedded in the relationship shown in Figures '7 and 8. The

surface of this body is rock-like and granular. The heating element isnow complete and ready to be cast into a sole plate. In the castingoperation the ceramic heating element is supported in the mold throughmeans of the projecting refractory bosses or holders 42 and 45. For thispurpose the metal casting mold (not shown) is provided with cavities forthe reception of the projecting holders and through means of thesecavities and holders the ceramic heating element is accurately locatedand held in proper position during the casting process. By holding theceramic heating element in this manner I provide against displacement orfloating of the element with respect to the mold and obtain the desireduniformity in wall thickness of the shell which is cast around theentire outer surface of the ceramic heating element with the exceptionof the projecting refractory holders. The refractory, granular surfaceof the heating element makes a good bond with the cast metallic shell. Acomplete sole plate casting is shown in Figures 1 to 6 inclusive, themetal sole plate being designated generally by 6|. It will be observedthat the metal sole plate is cast to a shape providing a comparativelythin sole plate portion 62. The outline shape of this sole plate portion62 determines the outline shape of the face 63 of the sole plate, whichface is flat and constitutes the ironing surface. The sole plate portion62 extends marginally beyond the ceramic heating element and the upperbody portion of the metallic sole plate body preferably conforms withthe exterior shape of the ceramic heating element so as to provide acomparatively thin enclosing shell structure. This construction providesa centrally located cavity or well 64 in the top of the sole plate forlocation of a thermostat element 65 which is shown diagrammatically indotted lines in Figure 3. While any suitable or preferred thermostatmeans may be employed in, conjunction with the switch for controllingthe electric current supply, to the heating element, I prefer athermostatic switch structure having a bimetallic thermostatic elementlocated close to the ironing surface so as to be quickly responsive tothe temperature thereof. I also prefer aluminum as the metal for thesole plate casting, but other suitable lightweight metal may be used.The use of aluminum not only reduces the weight but provides theadvantage of greater uniformtiy of temperature distribution due to itsgreater heat conductivity. With this construction the heat will beconducted away from the heating element in a short direct path to theface of the sole plate proper. This is advantageous in a flatironbecause it promotes quick heat transfer to the ironing surface withminimum of heat loss upwardly and it enables reduction in the operatingtemperatures of the heating element. Light weight is highly desirablebecause it makes ironing easier and avoids fatigue. A further advantageis in the embedded unitary structure as compared with prior sole plateswhich employ a heating element held in position by means of a toppressure plate or the like. Also, it is believed that a constructionsuch as herein disclosed is less expensive than prior constructionswhich use mica as an insulator and which require machine operations toaccommodate the top pressure plate to the sole plate proper.

It is believed that the foregoing conveys a clear understanding of theobjects prefaced above.

In the practice of my invention modifications may be made in the form ofthe resistor element and in the circuitous arrangement thereof as wellas in the form of the molded ceramic body in which the resistor isembedded. While I have shown a particular embodiment of the invention itwill be understood that the I do not wish to be limited thereto sincemany modifications may be made and I therefore contemplate by theappended claims to cover any such modifications as fall within the truescope and spirit of my invention.

I claim:

1. A sole plate for an electric iron comprising a ceramic skeleton-likebody molded to provide a loop outer body portion of relatively smallcross section conforming substantially with the outline shape of a soleplate ironing face and an inner loop body portion of similar crosssection extending within said outer body portion and laterally spacedfrom the adjacent outer body portion except for one section common tosaid inner and outer body portions, additional narrow bridging bodyportions connecting said outer and inner portions. a resistor embeddedin said outer and inner body portions and extending from one of saidbody portions to another through said common section, refractory bossesembedded in said bridging body portions and projecting beyond thesurface thereof, and a metallic shell cast around said ceramic body.

2. A heating element for the sole plate of an electric iron comprising aceramic skeleton-like body of vitrified cementitious material having theproperties of high electrical resistivity and high thermal conductivity,and a helical electrical resistor wire embedded in said body, said wirearranged to extend substantially entirely around the peripheral portionof the heating element and in a circuitous path entirely within andspaced inwardly from said peripheral portion, said ceramic bodyconforming to the described path of the helical wire and having narrowbridging portions for maintaining the peripheral portion of the ceramicbody and the portion associated with the inner circuitous path in fixedrelationship, said bridging portions providing a path for portionsofsaid wire other than that disposed in the outer peripheral portion andthe inner circuitous path, said ceramic body being defined so that thereare provided substantial open spaces intermediate the relatively narrowbody portions in which the wire is embedded, a plurality of bridgingportions located at a forward position on the element and anotherplurality located rearwardly thereof, and a refractory boss embedded ineach of such bridging portions and projecting above the same to providea locating portion, the rear refractory bosses also serving asinsulators for the terminal ends of the resistor Wire.

HERBERT F. STORM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

